Disclosed herein is a seatback frame forming a frame of a seat back for a vehicle seat, and particularly a seatback frame which can reduce an applied load at the time of a vehicle collision.
Countermeasures have been taken in a conventional vehicle seat against a phenomenon in which a seated occupant is moved rearward to sink into the seat at the time of a vehicle rear-end collision (hereinafter, the phenomenon will be referred to as a sinking phenomenon). Among the countermeasures, for example, techniques disclosed in JPH10-119616A and JP2005-088618A have been developed as countermeasures to reduce a load applied to a seated occupant in a sinking phenomenon. The techniques of JPH10-119616A and JP2005-088618A have been both developed in consideration for an amount of sinking (i.e., a rearward movement) of the chest of the seated occupant at the time of the sinking phenomenon.
Briefly, as illustrated in FIG. 9, the amount of sinking of the chest of the seated occupant (shown by the white thick arrow in FIG. 9) at the time of the sinking phenomenon is larger compared to that of another portion such as the neck or the low back. Due to a difference between such amounts of sinking, the seated occupant's posture turns to a so-called slouching posture, and forward loads (shown by the black thick arrows in FIG. 9) each as a reaction force from the seat are applied to the seated occupant. Such forward load is an applied load at the time of a vehicle collision (the applied load will be hereinafter simply referred to as a load). FIG. 9 is a diagram illustrating a general sinking phenomenon, showing a state where the amount of sinking of the chest of the seated occupant is large.
For dealing with the above problem, a vehicle seat disclosed in JPH10-119616A is configured to include: an energy absorbing cassette arranged in a corresponding portion of a seat back to the chest of the seated occupant; and an energy absorbing body arranged in a predetermined position of a headrest. Further, in JPH10-119616A, rebound characteristics (rebound speeds, rebound start timing) of the energy absorbing cassette and the energy absorbing body are adjusted relative to a seatback pad and the headrest while their characteristics are taken into consideration. Therefore, a difference between a rebound speed of the head of the seated occupant and a rebound speed of the chest of the seated occupant when the head and the chest rebound, and a difference between the rebound start timing of the head of the seated occupant and the rebound start timing of the chest of the seated occupant are reduced. According to such configuration, a load acting on the seated occupant at the time of a vehicle collision can be effectively reduced.
Further, in a vehicle seat disclosed in JP2005-088618A, a pivotal frame is provided in a seatback frame. At the time of a vehicle rear-end collision, a lower portion of the pivotal frame pivots in an arc upward and rearward from the front side of the seatback frame while an upper portion of the pivotal frame pivots forward. Meanwhile, when the upper portion of the pivotal frame pivots forward, the headrest moves forward along with such forward pivotal movement of the upper portion. Furthermore, in JP2005-088618A, when the chest of the seated occupant is sunk into the seat back by impact inertia at the time of the vehicle rear-end collision, the lower portion of the pivotal frame pivots in an arc by using the sinking movement. In conjunction with such pivotal movement of the lower portion, the headrest moves correspondingly to a movement of the head of the seated occupant at the time of the vehicle rear-end collision. According to such configuration, at the time of the sinking phenomenon, a difference between the amount of sinking of the chest of the seated occupant and an amount of sinking of the head of the seated occupant can be reduced. As a result, a load acting on the seated occupant at the time of the vehicle collision can be effectively reduced.
However, in JPH10-119616A and JP2005-088618A, the energy absorbing cassette and the energy absorbing body or the pivotal frame and its accessory components are required in order to reduce the load to the seated occupant at the time of the sinking phenomenon. Therefore, the configuration of the seat may be complicated, and the number of components may increase. Consequently, the configuration is required to be simplified as a countermeasure to reduce the load at the time of the vehicle collision.
Accordingly, the seatback frame disclosed herein is made in view of the above problem, and provides a frame which serves as a seatback frame forming a frame of a seat back for a vehicle seat and which is simply configured to reduce a load applied to a seated occupant at the time of a vehicle collision.